A variety of proteins having affinities for an immunoglobulin and/or an immune complex are known and, among them, Protein A and Protein G have been particularly well studied. Both Protein A and Protein G have high affinities for an immunoglobulin and/or an immune complex, but whereas the affinity of Protein A for IgG3 is low, Protein G binds to IgG3 (Japanese Patent No. 02764021). Furthermore, the Protein G gene has been shown to have nucleotide sequences coding for 3 kinds of peptide binding to an immunoglobulin and/or an immune complex, which are called C1, C2 and C3, and the corresponding amino acid sequences are as shown under the SEQ ID NOs:3, 4 and 5 of the sequence listing (Japanese Patent No. 02764021). C1 (SEQ ID NO:3)
C1 (SEQ ID NO:3)Thr Tyr Lys Leu Ile Leu Asn Gly Lys Thr Leu Lys Gly Glu Thr Thr Thr Glu Ala Val Asp Ala Ala Thr Ala Glu Lys Val Phe Lys Gln Tyr Ala Asn Asp Asn Gly Val Asp Gly Glu Trp Thr Tyr Asp Asp Ala Thr Lys Thr Phe Thr Val Thr Glu C2 (SEQ ID NO:4)Thr Tyr Lys Leu Val Ile Asn Gly Lys Thr Leu Lys Gly Glu Thr Thr Thr Glu Ala Val Asp Ala Ala Thr Ala Glu Lys Val Phe Lys Gln Tyr Ala Asn Asp Asn Gly Val Asp Gly Glu Trp Thr Tyr Asp Asp Ala Thr Lys Thr Phe Thr Val Thr Glu C3 (SEQ ID NO:5)Thr Tyr Lys Leu Val Ile Asn Gly Lys Thr Leu Lys Gly Glu Thr Thr Thr Lys Ala Val Asp Ala Glu Thr Ala Glu Lys Ala Phe Lys Gln Tyr Ala Asn Asp Asn Gly Val Asp Gly Val Trp Thr Tyr Asp Asp Ala Thr Lys Thr Phe Thr Val Thr Glu
Furthermore, from an X-ray structure analysis of a complex composed of C2 and IgG (Fc), it has been clearly shown that Glu26, Lys27, Lys30, Gln31, Asn34, Asp39, Glu41 and Trp42 of C2 bond to Fc (Sauer-Eriksson AE, Kleywegt GJ, Uhlen M, Jones TA Crystal structure of the C2 fragment of streptococcal protein G in complex with the Fc domain of human IgG. Structure 1995 Mar. 15; 3 (3): 265–78).
One important possible application of a peptide or protein having affinities for an immunoglobulin and/or an immune complex is its application to an adsorbent for the purification, isolation and/or removal of an immunoglobulin and/or an immune complex. However, we found that said C1, C2 and C3 peptides are too thermally unstable to withstand the sterilization by autoclaving, and apt to sustain marked depressions in the binding activity by radiation sterilization.